This invention relates to the field of separable, compliant electrical connectors.
Separable, compliant electrical connectors are typically used for test and burn-in of chips and other electrical components. Typically, chip packages have a large number of closely spaced contacts that must be brought into electrical contact with electrical contacts on a printed circuit board or a like substrate. It is desirable that the contact be low resistance and low inductance while at the same time being quick and simple to accomplish.
Connectors commonly used for this task include pogo pin connectors that include an array of vertically-compliant conductive pins that contact the chip on one end and a substrate on the other end. The vertical compliance is accomplished with conductive springs. Although these pogo pin connectors successfully separably interconnect electrical devices with sufficient vertical compliance for the task, they are expensive and exhibit substantial inductance, which limits the signal transfer rate through the pins. This can be a limiting factor for the types of devices tested as well as the time it takes to conduct the test. Also, the pins of pogo pin connectors require a relatively large spacing between pins, which limits the pitch of the contacts.
It is therefore an object of this invention to provide a pin-array, separable, compliant electrical contact member.
It is further object of this invention to provide such an electrical contact member that is relatively simple and inexpensive.
It is a further object of this invention to provide such an electrical contact member that has a low inductance.
It is a further object of this invention to provide such an electrical contact member that is relatively robust.
It is a further object of this invention to provide such an electrical contact member that has its contact pins spaced at a very fine pitch.
Anisotropic Conductive Elastomer (ACE) as the term is used herein is a composite of conductive metal particles in an elastomeric matrix that is constructed such that it conducts along one axis only. In general, this material is made to conduct through its thickness. ACE is generally produced by mixing magnetic particles with a liquid resin, forming the mix into a continuous sheet, and curing the sheet in the presence of a magnetic field. This results in the particles forming columns through the sheet thickness that are substantially perpendicular to the major surfaces of the ACE sheet. These columns are electrically conductive, creating anisotropic conductivity.
This invention features a pin-array, separable, compliant electrical contact member for separably, electrically interconnecting a first electrical device having electrical contacts to a second electrical device having electrical contacts. The inventive device includes a probe housing having a thickness, and defining a plurality of openings through the thickness, one or more pin probes, each pin probe located in and protruding from an opening in the probe housing, and each defining an enlargement larger than the opening in which the pin is located, to inhibit lateral pin motion, and also prevent the pins from being removed from their openings vertically in at least one direction, and a layer of ACE adjacent to the probe housing and comprising a plurality of conductive chains of particles through the layer thickness and aligned generally perpendicularly to the layer""s major surfaces. One end of the pin probes are in contact with the electrical contacts of the first electrical device, and the other ends of the pin probes are in compressive contact with a major surface of the ACE layer. The other major surface of the ACE layer is in contact with the electrical device, such that electrical signals are passed between the two electrical devices through the pin probes and the ACE layer.
The pin enlargements may be on the ends of the pins that are in contact with the ACE layer, which provides the further benefit that the contact area at the ACE major surface is increased. This can be used to match the pin/ACE contact size and shape to that of the underlying board contact. The pin ends that are in contact with the ACE layer are preferably substantially flat. The probe housing may be a single thin or thick layer, or may comprise two or more spaced layers, to accomplish a desired thickness. The electrical contacts on the first electrical device may have a particular end shape (for example, partially spherical), and the ends of the pins in contact with them may have a complementary shape to maximize contact area and minimize contact damage.
The ACE layer may be coupled to the probe housing, for example with an adhesive or with mechanical members. In one embodiment, the ACE layer is held in tension by the probe housing. The ACE layer may define one or more open areas, and the probe housing may in such case define an opening above the ACE layer discontinuity, to allow the contact member to be placed on a substrate with components protruding from its surface. The pin enlargements may be captured within the probe housing.
The probe housing may comprise vertically spaced layers defining a cavity with in which the pin enlargements are captured. The electrical contact member may further comprise a frame to which the ACE layer is coupled. T he ACE layer maybe held in tension by th e frame. The probe housing may fit within the frame.
The electrical contact member may further comprise means for aligning the probe housing to the second electrical device, which may be accomplished with alignment pins. The electrical contact member may then further comprise an alignment frame, wherein the alignment frame is coupled to the second electrical device with alignment pins, and the probe housing is coupled to the alignment frame by alignment pins. The probe housing may be vertically compressible. The probe housing may comprise one or more vertically-compliant members such as springs to provide vertical compliance to the housing. The top surface of the probe housing may be above the tops of the pins when it is not compressed, to protect the pins from damage.